From limited experience, it seems that while short-term memory might present difficulties, some 'residents' often have fair long-term memory, and can remember the songs of their youth. You could try a song or two from sixty years ago.
Assuming that you are in England, the monologues that were recited by Stanley Holloway are often remembered with glee, and easily obtained online from 'Make 'em Laugh.' Much easier to learn than songs, too, without accompaniment.

And 'well done you' for doing it.